java.lang.IllegalArgumentException: cannot add to layout: constraint mu
be a string (or null) at java.awt.BorderLayout.addLayoutComponent(BorderLayout.java:401) at javax.swing.JRootPane$1.addLayoutComponent(JRootPane.java:453) at java.awt.Container.addImpl(Container.java:482) at java.awt.Container.add(Container.java:345) at undefined.eMailFrame.add(eMail.java:118) at undefined.eMailFrame.(eMail.java:67) at undefined.eMail.main(eMail.java:12)